This invention relates generally to ferroelectric memories. More particularly, the present invention relates to a wafer-level diagnostic test for characterizing the performance of integrated circuit ferroelectric memories.
A method of testing ferroelectric capacitors is set forth in an article entitled "Capacitor Test Simulation of Retention and Imprint Characteristics for Ferroelectric Memory Operation" presented at the ISIF conference, Mar. 18-20, 1996 in Phoenix, Ariz., and in co-pending patent application Ser. No. 08/616,913 assigned to the present assignee, Ramtron International Corporation, entitled "A method of Measuring Retention Performance and Imprint Degradation of Ferroelectric Films", both of which are hereby incorporated by reference.
In the above-referenced article and patent application, the test method disclosed therein measures same state and opposite state charge, which is extremely useful in characterizing the electrical performance of ferroelectric capacitors and films. However, ferroelectric capacitor and film performance is not necessarily correlated to integrated circuit ferroelectric memory performance. The results of this test cannot, therefore, be relied upon to accurately predict the behavior of a ferroelectric memory at wafer level. This is due to the myriad of other factors affecting performance related to the design of the memory and the semiconductor processing steps used in fabricating the memory, as well as other factors. Each of these factors can affect memory performance either directly or by interacting with the underlying ferroelectric capacitor performance.
What is desired, therefore, is a comprehensive diagnostic test for evaluating and characterizing the electrical performance of integrated circuit ferroelectric memories.